Teeth are the hardest substance in the human body, harder than any bone.

The longer version

Enamel is a densely packed mineral crystal with almost no living cells in it, which is what gives a tooth its hardness. The crystals are laid down during development by cells that later disappear, so the finished layer cannot regrow itself.

Beneath it sits dentine, which is softer and filled with tiny channels leading toward the pulp, and that inner tissue contains nerves and blood vessels. Enamel handles the grinding and biting forces, while the softer layers absorb shock and, when exposed, transmit sensation. Hardness here means resistance to scratching and wear rather than resistance to cracking. Acids produced by bacteria in the mouth can dissolve that mineral over time, which is why decay begins as a soft spot.

Where this entry sits

These facts look at how the human body works in ordinary moments, from breathing and blinking to balance and sleep. They focus on anatomy, senses, and small reactions that happen constantly without any conscious effort. The full list sits on the Human Body page, where every entry is listed in order.